U.S. patent number 5,591,780 [Application Number 08/633,325] was granted by the patent office on 1997-01-07 for low odor amine catalysts for polyurethane flexible slabstock foams based on polyester polyols.
This patent grant is currently assigned to Air Products and Chemicals, Inc.. Invention is credited to Mark E. Harakal, Steven P. Hulme, Krunoslav Muha.
United States Patent |
5,591,780 |
Muha , et al. |
January 7, 1997 |
Low odor amine catalysts for polyurethane flexible slabstock foams
based on polyester polyols
Abstract
A method for preparing a polyester flexible slabstock
polyurethane foam which comprises reacting an organic
polyisocyanate and a polyester polyol in the presence of a blowing
agent, optionally a cell stabilizer and a catalyst composition
consisting essentially of N-methylimidazole or
1,2-dimethylimidazole, or both.
Inventors: |
Muha; Krunoslav
(Henstedt-Ulzburg, DE), Hulme; Steven P.
(Macclesfield, GB2), Harakal; Mark E. (Hurricane,
WV) |
Assignee: |
Air Products and Chemicals,
Inc. (Allentown, PA)
|
Family
ID: |
22801500 |
Appl.
No.: |
08/633,325 |
Filed: |
April 17, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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215067 |
Mar 18, 1994 |
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Current U.S.
Class: |
521/128; 521/129;
521/172 |
Current CPC
Class: |
C08G
18/2027 (20130101); C08G 18/42 (20130101); C08G
2110/0008 (20210101) |
Current International
Class: |
C08G
18/42 (20060101); C08G 18/20 (20060101); C08G
18/00 (20060101); C08G 018/20 () |
Field of
Search: |
;521/128,129,172 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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671012 |
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Oct 1964 |
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BE |
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0451826 |
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Oct 1991 |
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EP |
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0566247 |
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Oct 1993 |
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EP |
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Primary Examiner: Foelak; Morton
Attorney, Agent or Firm: Leach; Michael Marsh; William
F.
Parent Case Text
This application is a continuation of application Ser. No.
08/215,067 filed on Mar. 18, 1994.
Claims
We claim:
1. In a method for preparing a flexible polyurethane slabstock foam
which comprises reacting an organic polyisocyanate and a polyester
polyol in the presence of a blowing agent, optionally a cell
stabilizer, and a catalyst composition, the improvement for
providing a flexible open-celled polyurethane slabstock foam which
comprises employing a catalyst composition consisting essentially
of N-methylimidazole or 1,2-dimethylimidazole, or both.
2. The method of claim 1 in which the catalyst composition consists
essentially of N-methylimidazole.
3. The method of claim 1 in which the catalyst composition consists
essentially of 1,2-dimethylimidazole.
4. The method of claim 1 in which the catalyst composition is used
in combination with a tertiary amine, organotin or carboxylate
urethane catalyst.
5. The method of claim 2 in which the catalyst composition is used
in combination with a tertiary amine, organotin or carboxylate
urethane catalyst.
6. The method of claim 3 in which the catalyst composition is used
in combination with a tertiary amine, organotin or carboxylate
urethane catalyst.
7. In a method for preparing a flexible polyurethane slabstock foam
which comprises reacting toluenediisocyanate and a polyester polyol
in the presence of water as a blowing agent, optionally a cell
stabilizer, and a catalyst composition, the improvement for
providing a flexible open-celled polyurethane slabstock foam which
comprises employing a catalyst composition consisting essentially
of N-methylimidazole or 1,2-dimethylimidazole, or both.
8. The method of claim 7 in which the catalyst composition consists
essentially of N-methylimidazole.
9. The method of claim 7 in which the catalyst composition consists
essentially of 1,2-dimethylimidazole.
10. The method of claim 7 in which the catalyst composition is used
in combination with a tertiary amine, organotin or carboxylate
urethane catalyst.
11. The method of claim 8 in which the catalyst composition is used
in combination with a tertiary amine, organotin or carboxylate
urethane catalyst.
12. The method of claim 9 in which the catalyst composition is used
in combination with a tertiary amine, organotin or carboxylate
urethane catalyst.
Description
TECHNICAL FIELD
The present invention relates to the use of imidazoles as catalysts
for producing polyurethanes.
BACKGROUND OF THE INVENTION
The polyurethane industry is coming under increased pressure from
many environmental groups due to emissions of chemicals during the
production of foam, worker exposure to these chemicals, and
ultimately the recyclability of the final polyurethane materials.
During the foaming process, polyols are reacted with
polyisocyanates in the presence of blowing agents, i.e., water and
secondary materials such as chlorofluorocarbons (CFCs), methylene
chloride, and the like. An integral part of the production of these
foams is the inclusion of silicone surfactants to stabilize the
developing foam cells and catalysts to both initiate the foam
reaction (blowing reaction) and effect cure of the developing foam
matrix (gelling reaction). Typical catalysts used to initiate the
blow and gel reactions in polyether polyol flexible foam
formulations are bisdimethylaminoethylether and triethylenediamine
(TEDA). Both these molecules possess tertiary amine
functionality.
As compared to flexible polyether polyol formulations, foams
formulated from polyester polyols have significantly higher
reactivity that require the use of different types of catalysts. A
polyester polyol differs from a polyether polyol in terms of its
functionality, molecular weight and the nature of the hydroxyl
groups. Polyester polyols contain highly reactive primary alcohols,
while polyether polyols usually contain less reactive secondary
alcohols.
Of greater significance to the selection of a catalyst in these
systems is the use of different ratios of toluenediisocyanate (TDI)
isomers. The difference in reactivity toward the blowing reaction
(isocyanate and water reaction to form CO.sub.2) is a result of the
2,4-TDI isomer being more reactive to the water molecular than the
2,6-TDI isomer due to steric hindrance in the latter. The
difference in reactivity toward the gelation reaction (isocyanate
and polyol reacting to form polyurethane linkages) between the
isomers is even greater due to the size of the polyol chains
restricting mobility of the OH functional group. Thus the
quantitative effect of steric hindrance of the 2,6-TDI isomer is
increased. As gelation is reduced significantly with the 2,6-TDI
isomer compared to the 2,4-TDI isomer, additional urea formation is
feasible via the continued blowing reaction resulting in enhanced
cell openness. The combination of reduced activity, substantially
reduced gelation and increased cell opening from urea formation
leads to the need for a relatively strong gelation catalyst when
higher amounts of 2,6-TDI isomer are used.
Only a few catalyst molecules allow for foam formation with desired
smooth reaction profiles and without final foam shrinkage. By
smooth reaction profile, we mean a low maximum rise rate of the
developing foam which leads to smooth processability resulting in
minimized density and air flow gradients, reduced voids and
split-free as well as pinhole-free foam. The catalyst must work
synergistically with the silicone surfactant providing for good
processing latitude that results in smooth rise profiles, minimal
recession, consistent density distribution and sufficient cell
openness. A catalyst for polyester slabstock foam must have strong
blowing capabilities in TDI 80/20 (2,4TDI/2,6-TDI) formulations.
The catalyst should have well balanced blow/gelation
characteristics for formulations based on mixtures of TDI 80/20 and
TDI 65/35, while stronger gelation characteristics are required for
formulations based on TDI 65/35. In formulations based upon TDI
80/20, the blowing catalysts utilized are typically based upon
morpholine structures, such as N-ethylmorpholine (NEM) or
N-methylmorpholine NMM), and 1,2-dimethylpiperazine (DMP) with
N-cetylamine used as a co-catalyst to effect gelation. In mixed
isocyanate (TDI 80/20 and TDI 65/35) or TDI 65/35 isocyanate
systems, the catalyst must have more balanced blow to gelation
properties; for these formulations, benzyldimethylamine (BDMA) is
typically used as a catalyst. Both the NEM and BDMA type catalysts
provide for broad processing latitude with optimal foam
characteristics. Physical properties of the foam must include a
scorch-free appearance (no yellowing) with fine cell structures
free of pinholes which is required for flame lamination to
textile.
The problem confronting the industry is that although these
catalysts provided for optimum reaction profiles in the polyester
polyol slabstock systems, they also possess negative attributes in
terms of their odor, corrosivity and handling, and toxicological
properties. These negative attributes may be significant issues in
a foaming operation.
During a foaming process the liquid chemicals are laid down through
a variety of techniques onto a moving conveyor contained within a
channel. As the foam ingredients react, the exotherm results in the
vaporization of blowing agents and the foam rises within the moving
channel. During the initial phase of foam rise there is a blowoff
of chemicals from the foam, most notably TDI in the vapor state,
CO.sub.2 from the reacting water and also low volatility additives.
To reduce worker exposure to these potentially harmful vapors, the
first stage of the continuous foaming process is done in an
enclosed ventilated area; however, due to the speed with which many
manufacturers run production to maximize output, the developing
foam is enclosed within this area for only several minutes.
Directly after the stage,. the foam is cut and moved along
conveyors to a storage area. During this latter phase of
production, plant workers are continuously exposed to any vapors
emitted from the cut foam. Since maximum temperatures are not
reached in the foam until about 10 hours after production, higher
molecular weight additives such as the catalysts will start to
migrate out of the foam into the surrounding environment. In the
case of catalysts such as NEM, NMM and BDMA, vapor pressures are
sufficient to volatilize amine during this cutting and storage
process.
There are several facets to this problem, the first of which is
that these materials possess extremely strong odors not unlike that
of ammonia. As the catalysts are potential lacrimators, a worker in
close proximity to the foam would suffer from extreme tearing.
Additional problems with the use of these materials is that the
co-catalyst necessary to obtain the desired curing profiles in the
foam are strong irritants, so that workers involved in any handling
of either the pure catalyst or final foam may develop skin
irritation as a result of this exposure. The residual odor of
products such as NEM, NMM, and BDMA can extend beyond the curing
stage into the final cutting and fabrication points of the
facility, thereby exposing additional workers to the odor and
harmful side effects of the catalyst. A polyester flexible
slabstock foam production facility is notable by the continuous
emanation of amine odors at all times, both inside and around the
plant.
Accordingly, there has been extreme pressures on the suppliers of
catalysts to the polyester polyol flexible slabstock industry to
produce new, lower odor versions of the catalysts. Prior attempts
to develop new catalysts have included derivatives of morpholine as
exemplified by N-methoxyethylmorpholine, N-methoxypropylmorpholine
and 2,2-dimorpholinodiethylether. However, in order to achieve the
same reactivity as the conventional polyester catalysts (NEM, NMM
and BDMA), it is necessary to co-catalyze these systems with other
amines such as dimethylpiperazine. Piperazine molecules have a
reasonably strong odor and are known irritants that can cause
adverse toxicological and health effects such as blue haze.
Other attempts at replacing conventional polyester catalysts have
resulted in compromises, either in terms of system reactivity or
some degree of odor or toxicological effects. Conventional gelation
catalysts such as dimethylcyclohexylamine have been used either
partially or completely as a replacement for NEM. This molecule is
very attractive and provides for excellent gelation in polyesters
systems; if anything, the use levels of this product must be
carefully metered to maintain desired system reactivity. However,
the odor from this catalyst rivals that of NEM.
To date there have been no realistic solutions presented to the
market that address the issues of balanced reactivity and reduced
worker exposure during the production of polyester polyol-based
polyurethane foam. Thus there is a need in the industry for low
odor catalysts that manifest a smooth reaction profile comparable
to the current industry standard catalysts NEM and BDMA, i.e.,
drop-in replacements for NEM and BDMA.
In addition, processability of the reaction streams of the
polyurethane system is critical. Due to the high viscosity of the
polyol-containing component (premix) of the polyurethane system,
catalysts must be liquid at about 15.degree. C. or soluble in a
suitable carrier so that it may be delivered into the
polyol-containing component for the reaction process in liquid
phase.
U.S. Pat. No. 3,152,094 discloses the use of certain imidazoles in
the production of polyurethane foams. Example III shows the use of
2-methylimidazole in a polyester polyol flexible polyurethane foam
formulation.
U.S. Pat. No. 3,448,065 discloses methods for producing
polyurethane foams using N-hydroxyalkyl substituted imidazoles.
U.S. Pat. No. 4,234,693 discloses a process for making polyurea
foams which comprises reacting an organic polyisocyanate with at
least a chemically equivalent amount of water in the presence of an
imidazole compound, such as 1-alkyl and 1,2-dialkyl imidazoles as
sole catalysts. Polymeric polyols are suggested as being useful in
reducing the friability of the foams.
BE 671,012 discloses preparing polyurethane foams using 1,2-di
substituted imidazoles as catalysts to prepare flexible and rigid
polyurethane foams. Examples show the effectiveness of the catalyst
in polyether flexible and rigid foam systems, but do not show any
polyester polyol systems.
U.S. Pat. No. 5,104,907 discloses the use of certain substituted
imidazoles for producing a high resilience polyurethane foam in
which the polyisocyanate contains diphenylmethane diisocyanate and
the blowing agent is water and/or a halogenated hydrocarbon.
EP 0 451 862 disclosed a process for producing flexible
polyurethane foam by the reaction of a polyol with a polyisocyanate
in the presence of an amine catalyst, a blowing agent, and a foam
stabilizer, the amine catalyst comprising at least one of the
imidazoles represented by a certain generic formula.
SUMMARY OF THE INVENTION
The present invention provides a catalyst composition for the
production of foamed polyurethanes from polyester polyols. The
catalyst compositions comprise N-methylimidazole
(1-methylimidazole) or 1,2-dimethylimidazole, MI and DMI,
respectively.
As an advantage of these catalysts there is significantly reduced
odor during the foaming process as well as from the finished foam
product. Significantly, these catalysts provide smooth rise
profiles leading to predominantly open-celled foam and are easily
delivered as solutions in carriers which are common to polyurethane
processes.
Thus, there is provided low odor catalysts that manifest a smooth
reaction profile comparable to the current industry standard
catalysts NEM and BDMA, i.e., drop-in replacements for NEM and
BDMA.
Also provided is a method for preparing a polyester flexible
slabstock polyurethane foam which comprises reacting an organic
polyisocyanate and a polyester polyol in the presence of a blowing
agent, optionally a cell stabilizer, and a catalyst composition
consisting essentially of N-methylimidazole or
1,2-dimethylimidazole, or both.
DETAILED DESCRIPTION OF THE INVENTION
The catalyst compositions according to the invention can catalyze
(1) the reaction between an isocyanate functionality and an active
hydrogen-containing compound, i.e. an alcohol, a polyol, an amine
or water, especially the urethane (gelling) reaction of polyol
hydroxyls with isocyanate to make polyurethanes and the blowing
reaction of water with isocyanate to release carbon dioxide for
making foamed polyurethanes, and/or (2) the trimerization of the
isocyanate functionality to form polyisocyanurates.
The polyurethane products are prepared using any suitable organic
polyisocyanates well known in the art including, for example,
hexamethylene diisocyanate, phenylene diisocyanate, toluene
diisocyanate ("TDI") and 4,4'-diphenylmethane diisocyanate ("MDI").
Especially suitable are the 2,4- and 2,6-TDI's individually or
together as their commercially available mixtures. Other suitable
isocyanates are mixtures of diisocyanates known commercially as
"crude MDI", also known as PAPI, which contain about 60% of
4,4'-diphenylmethane diisocyanate along with other isomeric and
analogous higher polyisocyanates. Also suitable are "prepolymers"
of these polyisocyanates comprising a partially prereacted mixture
of a polyisocyanate and a polyether or polyester polyol.
Suitable polyester polyols as a component of the polyurethane
composition for flexible slabstock foams are well known in the
industry. Illustrative of such suitable polyester polyols for
flexible slabstock foams are those produced by reacting a
dicarboxylic and/or monocarboxylic acid with an excess of a diol
and/or polyhydroxy alcohol, for example, adipic acid, glutaric
acid, succinic acid, phthalic acid or anhydride, and/or fatty acids
(linolic acid, oleic acid and the like) with diethylene glycol,
ethylene glycol, propylene glycol, dipropylene glycol,
1,4-butanediol, trimethylolpropane and/or pentaerythritol.
Other typical agents found in the polyurethane foam formulations
include chain extenders such as ethylene glycol and butanediol;
crosslinkers such as diethanolamine, diisopropanolamine,
triethanolamine and tripropanolamine; blowing agents such as water,
methylene chloride, trichlorofluoromethane, and the like; and
optionally cell stabilizers such as silicones. Many other additives
such as flame retardants, dyes, pigments and oils can also be
included.
A general polyester polyol polyurethane flexible slabstock foam
formulation having a 8-80 kg/m.sup.3 density and containing the
catalyst composition according to the invention would comprise the
following components in parts by weight (pbw):
______________________________________ Flexible Foam Formulation
pbw ______________________________________ Polyester Polyol 100
Silicone Surfactant 0-2.5 Blowing Agent 1-9 Organotin Catalyst
0-0.2 Imidazole Catalyst 0.2-2 Isocyanate Index 70-115
______________________________________
The catalyst composition consists essentially of imidazoles of the
following formula: ##STR1## where R is hydrogen or methyl. The
imidazoles may be used as the sole catalysts, in combination with
one another or in combination with other tertiary amine, organotin
or carboxylate urethane catalysts well known in the urethane
art.
The imidazoles which are commercially available from BASF AG
Ludwigshafen, Germany are conveniently delivered as pure compounds.
The catalysts are conveniently delivered to the polyol-containing
premix as solutions, preferably in carriers such as alcohols and
polyols. The most preferred carrier is dipropylene glycol (DPG).
The polyurethane industry requires that reactants be delivered into
the reaction process in liquid phase. Most foam producers, if not
all, will not use solid materials unless they are soluble
(.gtoreq.150 mg/ml) in solvent appropriate for the urethane
system.
A catalytically effective amount of the catalyst composition is
used in the polyurethane formulation. More specifically, suitable
amounts of the catalyst composition (solids) may range from about
0.01 to 10 parts, preferably 0.1 to 3 parts, per 100 parts
polyester polyol (phpp) in the polyurethane formulation.
These catalyst compositions afford the advantage of significantly
reduced odor during the foaming process as well as from the
finished product. Amine emissions from the plant can also be
greatly reduced allowing for a safer working environment.
Additionally, these catalysts provide smooth rise profiles leading
to predominantly open-celled foam and are easily delivered as
solutions in carriers which are common to polyurethane foam
processes.
EXAMPLE 1
In this example, the various imidazoles were delivered at room
temperature into the polyester polyol flexible slabstock foam
reaction mixture of Table 1. Any imidazole which was non-liquid at
room temperature was introduced in a suitable carrier, such as DPG.
MI and DMI were used as 50% solutions in DPG. Some imidazoles were
not soluble in such diluents and thus were deemed undesirable and
not evaluated. Reaction profiles were obtained using ultrasonic
rate of rise equipment. The use level of each catalyst shown in
Table 2 was such as to achieve a rise time of about 85 seconds in
each instance, since that is the time required by a typical
conveyor line speed.
TABLE 1 ______________________________________ Pbw
______________________________________ Desmophen 2200 polyester
polyol.sup.a 100 DABCO .RTM. DC 5526 silicone surfactant 1.5 Water
4 Catalyst see Table 2 Desmodur T-80 Isocyanate.sup.b Index 95
______________________________________ .sup.a Polyester polyol from
Bayer AG. .sup.b TDI 80/20 from Bayer AG.
TABLE 2 ______________________________________ Use Level Rise Time
Max. Rise Speed Airflow Catalyst (pphp) (sec) (mm/sec) (m.sup.3
/min) ______________________________________ BDMA 1.0 85 5.85 0.048
NEM 1.5 85 5.70 0.051 MI 0.55 85 5.60 0.057 DMI 0.35 84 5.50 0.050
IBMI 0.40 84 6.10 0.045 BMI 0.75 86 6.20 0.043 CEMI 1.00 86 6.20
0.043 ______________________________________ BDMA --
benzyldimethylamine NEM -- Nethylmorpholine MI -- Nmethylimidazole
DMI -- 1,2dimethylimidazole IBMI -- 1isobutyl-2-methylimidazole BMI
-- 1benzyl-2-methylimidazole CEMI --
1cyanoethlyl-2-ethyl-4-methylimidazole
The data in Table 2 shows clearly improved reactivity (smooth rise
profiles) for 1,2-DMI and MI compared to other imidazoles having
similar structures.
For a given rise time a lower maximum rise speed is desirable. Too
steep a profile will lead to difficult processing and may lead to
foam collapse. Other imidazoles such as 2-methylimidazole,
2-undecylimidazole and 2-heptadecylimidazole were not successfully
introduced to the reaction mixture due to insolubility. Besides the
favored reaction profiles obtained using both MI and DMI, greater
airflows were obtained compared to other imidazoles, another very
favorable outcome.
EXAMPLE 2
This example shows the use of DMI as a suitable polyester slabstock
catalyst allowing for reduced amine emissions. Emissions from
various ventilation points around an industrial plant for making
slabstock foam were measured while producing polyester polyol foam
with BDMA. A similar production run was performed using DMI as the
catalyst. While the emissions for BDMA ranged from 0.8 to 10.0
mg/Nm.sup.3, no DMI was detected.
STATEMENT OF INDUSTRIAL APPLICATION
The present invention provides imidazole urethane catalysts for use
in making polyester polyol-based flexible slabstock polyurethane
foams.
* * * * *